1. Field of the Invention:
The present invention relates to a fluid machine with an induction motor, and more particularly to a fluid machine having many types of design points which can be operated by the same induction motor.
2. Description of the Prior Art:
Heretofore, a voltage and a frequency to be supplied to a motor are uniquely determined at a site where the motor is used. In order to enable the motor to be common use, it has been customary to provide a design point where shaft powers (motor outputs) are the same and to vary a flow rate and a produced pressure.
FIG. 4 of the accompanying drawings shows the relationship between a flow rate (Q) and a head (H) of a conventional fluid machine with an induction motor. A pump, for example, will be described as a non-positive displacement fluid machine having such characteristics that the flow rate is proportional to the rotational speed, the produced pressure is proportional to the square of the rotational speed, and the shaft power is proportional to the cube of the rotational speed.
A motor .alpha. is combined with a pump A at a flow rate Q and a head H, a motor .beta. is combined with a pump B at a flow rate (1/K)Q and the head H, and the motor .alpha. is combined with a pump C at the flow rate (1/K)Q and the head KH, thereby handling three particular points. Thus, three particular points are handled by two types of motors and three types of pumps.
Various specifications at the particular points are shown in FIG. 4.
With the conventional fluid machine arrangement, however, it is necessary to have a fluid machine available at each of the particular points, as shown in FIG. 4, and a motor can be shared only at the same output point. As a result, the number of types of design points of a fluid machine is enormous as compared with the number of types of motors used.